fix issue #83 (Image Inside a Scrollable div Would not be Loaded)

src/echo.js

@@ -1,11 +1,20 @@
-(function() {
+(function (root, factory) {
+  if (typeof define === 'function' && define.amd) {
+    define(function() {
+      return factory(root);
+    });
+  } else if (typeof exports === 'object') {
+    module.exports = factory;
+  } else {
+    root.echo = factory(root);
+  }
+})(this, function (root) {
+
   'use strict';
 
   var echo = {};
-    var root = {};
 
-    var callback = function () {
+  var callback = function () {};
-    };
 
   var offset, poll, delay, useDebounce, unload;
 
@@ -35,7 +44,7 @@
 
   echo.init = function (opts) {
     opts = opts || {};
-        root = opts.viewport || this || (0,eval)('this')
+    root = opts.viewport || this || (0,eval)('this');
     var offsetAll = opts.offset || 0;
     var offsetVertical = opts.offsetVertical || offsetAll;
     var offsetHorizontal = opts.offsetHorizontal || offsetAll;
@@ -69,8 +78,8 @@
     var view = {
       l: 0 - offset.l,
       t: 0 - offset.t,
-            b: (root.innerHeight || root.clientHeight) + offset.b,
+      b: (root.innerHeight || document.documentElement.clientHeight) + offset.b,
-            r: (root.innerWidth || root.clientWidth) + offset.r
+      r: (root.innerWidth || document.documentElement.clientWidth) + offset.r
     };
     for (var i = 0; i < length; i++) {
       elem = nodes[i];
@@ -121,14 +130,6 @@
     clearTimeout(poll);
   };
 
-    if ((typeof module !== "undefined" && module !== null) && module.exports) {
-        module.exports = echo;
-    } else if (typeof define === 'function') {
-        define(function() {
   return echo;
-        });
-    } else {
-        root.echo = echo;
-    }
-}());
 
+});